Ive just seen that you have only had these piggies for a week.
When piggies are moved to a new home, they go through a period of reestablishing their relationship. This will take a couple of weeks.
While it remains normal dominance ie chasing, nipping etc (ie no actual fights) (nipping is a gesture of power but doesn’t break the skin, it isn’t a bite) then you don’t need to do anything and you can’t stop it - it’s something they will need to get through in their own time.
Provided they like each other and want to be together, then you will see this period of increased dominance, they will sort themselves out and then it will calm down. It’s only if there are underlying problems in their relationship and they actually decide they don’t want to be together that things may need to be reconsidered.
Bullying is a sustained behaviour which can see the under pig become withdrawn, depressed and potentially lose weight through not being able to eat, alsays chased out of hides not allowed to rest.
All you can really do is ensure they have plenty of space (150x60m for two sows), multiple and multi-exit hides so no piggy can get cornered and can get out of any hide. Hopefully everything will settle down soon.
Sows: Behaviour and female health problems (including ovarian cysts)
Bonding and Interaction: Illustrated social behaviours and bonding dynamics
Moody Guinea Pigs: Depression, Bullying, Aggression, Stress, Fear and Antisocial Behaviour